Ecophysiological Responses to Rainfall Variability in Grassland and Forests Along a Latitudinal Gradient in Italy

In the Mediterranean region, ecosystems are severely affected by climate variability. The
Italian Peninsula is a hot spot for biodiversity thanks to its heterogeneous landscape
and the Mediterranean, Continental, and Alpine climates hosting a broad range of plant
functional types along a limited latitudinal range from 40′ to 46′ N. In this study we
applied a comparative approach integrating descriptive statistics, time series analysis,
and multivariate techniques to answer the following questions: (i) do the climatic variables
affect Gross Primary Productivity (GPP), Reco, Water Use Efficiency (WUE), and ET to a
similar extent among different sites? (ii) Does a common response pattern exist among
ecosystems along a latitudinal gradient in Italy? And, finally (iii) do these ecosystems
respond synchronically to meteorological conditions or does a delayed response exist?
Six sites along a latitudinal, altitudinal, and vegetational gradient from semi-arid (southern
Italy), to a mountainous Mediterranean site (central Italy), and sub-humid wet Alpine
sites (northern Italy) were considered. For each site, carbon and water fluxes, and
meteorological data collected during two hydrologically-contrasting years (i.e., a dry
and a wet year) were analyzed. Principal Component Analysis (PCA) was adopted to
identify temporal and spatial variations in GPP, Ecosystem Respiration (Reco), WUE, and
Evapotranspiration (ET). The model outlined differences among Mediterranean semi-arid,
Mediterranean mountainous, and Alpine sites in response to contrasting precipitation
regimes. GPP, Reco, WUE, and ET increased up to 16, 19, 25, and 28%, respectively in
semi-arid Mediterranean sites and up to 15, 32, 15, and 11%, respectively in Alpine
sites in the wet year compared to the dry year. Air temperature was revealed to be
one of the most important variables affecting GPP, Reco, WUE, and ET in all the study
sites. While relative air humidity was more important in southern Mediterranean sites,
global radiation was more significant in northern Italy. Our work suggests that a realistic
prediction of the main responses of Italian forests under climate change should also
take in account delayed responses due to acclimation to abiotic stress or changing
environmental conditions.